Apparatus for observing the conduct of a projectile in a gun



y 1950 N. M. SMITH, JR., EIAL 2,514,297

APPARATUS FOR OBSERVING THE CONDUCT OF A PROJECTILE IN A GUN Filed March 3, 1943 4 Sheets-Sheet l lNVE NTORS NIOHOL s1 2 m 2 41%, 4 M F 2 F 9 H ,I, u 5 {In July 4, 1950 N. M. SMITH, JR., ETAL 2,514,297

APPARATUS FOR OBSERVING THE CONDUCT OF A PROJECTILE IN A GUN 4 Shee1:s. s

Filed March 3 1943 INVENTORS July 4, 1950 N. M. SMITH, JR., ETAL APPARATUS FOR OBSERVING THE CONDUCT OF A PROJECTILE IN A GUN 4 Sheets-Sheet 3 Filed March 3, 1943 m m F m WW WMR W8C H JAN/Ln ML f mm m y 1950 N M SMITH JR EI'AL 2,514,297

' CONDUCT APPARATI'JS FOR oBsEvIN THE OF A PROJECTILE IN A GUN Filed March 3, 1943 4- Sheets-Sheet 4 FIG. 11. i 27 FIG. :2.

45 t I E 5 54 ?\\I\\\ \\\I\\\ c 90 2 ,1: I: I 84 88 if- 84 \i i v VYJ ALLEN c o KER 1 M Patented July 4, 1950 Ni TED STES APPARATUS FOR OBSERVIN G THE CONDUCT OF A PROJECTILE IN A GUN Application March 3, 1943, Serial No- 27,876

1'? Claims.

This invention relates to indicating systems for use in determining the conduct of a projectile in a gun barrel. More particularly, the invention has reference toa novel system of this character in which an electrical potential is generated in the projectile when it is fired in the gun, the potential being utilized to operate an electrical indicating device. The new system is of simple form and may be operated readily to provide accurate measurements. The potential for operating the indicating device is generated in a pro-- jectile of novel construction which also forms part of the invention.

One object of the invention resides in the provision of a novel system for indicating phenomena associated with the movement of a projectile through a gun barrel, in which the indicator is operated by an electrical potential generated in the projectile by the action of a force resulting from firing the projectile, for example, a force due to the pressure from the explosion of the firing charge or to the set back of a member in the projectile. The new system comprises means in the projectile for generating an electrical potential, the generating means being preferably in the form of a pieZo-electric crystal which is com pressed by the above-mentioned force. An electrical-indicating device, which may be located remotely from the gun, is operated by the potential thus generated in the projectile. In the preferred construction, the potential is impressed across the indicating device by conducting means including a wire connected to one side of the generating means and extending from the nose of the projectile along the bore of the gun through the muzzle, and insulated from the gun, to one side of the indicating device, the other side of the device being connected through the gun and the projectile body to the other side or" the generating means. The wire in the gun bore may be coiled and the nose of the projectile provided with an insulated collector unit for receiving the wire as the projectile moves through the bore.

Another object of the invention is to provide a novel projectile having means which, when the projectile is fired, generates an electrical potential for use in measuring a force resulting from firing the projectile. A projectile made in accordance with the invention comprises an electrical potential generating means, such as a piece electric crystal, in the projectile body, and means for subjecting the crystal to a compression com-- mensurate with a force to be measured. The compressing means may include a member movable relative to the projectile body for exerting a force of set back against the crystal, or a piss ton actuated by the gaseous pressure due to. ex.-

plosion of the firing charge. Preferably, the. generating means has an electrical connection extendin from one side through the body and insulated from the body, the other side of the generating means being electrically connected to the. projectile body, whereby one side of an indicating device outside the gun may be connected through the gun bore or chamber to the insulated connection, and the other side of the gun which provides a conducting path to the projectile body;

The new system is easy and inexpensive to operate and provides an accurate and positive indication of phenomena associated with movement of the projectile along the gun barrel when the gun is fired. Since the. means for generating the indicating pulse is located. in the projectile itself, the system may be used with a gun of ordinary form and it is unnecessary to employ any special attachment on the gun. The pulse generating means in the projectile is of compact construction and maybe used in .a projectile of any desired form.

These and other objects of the invention may be better understood by reference to the following detailed description and the accompanying drawings, in which Fig. 1 is a diagrammatic view of one form oi the new indicatin system;

Fig. 2 is an enlarged perspective view of the nose portion of the projectile shown in Fig. 1;

Fig. 3 is an enlarged axial sectional View of the v upper portion of the part of the projectile shown in Fig. 2; V

Fig. 4 is a perspective view of the wire collector unit shown in Figs. 1, 2 and 3;

Fig. 5 is a similar View of the container for the electricity generating means shown in Fig, 3;

Fig. 6 is an exploded view of the electricity generating means; I

Fig. 7 is an axial. sectional View of part of a modified form of the new projectile, showing the electricity generating means, the wire collector unit and the electrical connections;

Figs. 8, 9 and 10 are perspective views of parts of the projectile shown in Fig. '7; and

Figs. 1 1 and 12 are axial sectional views of two other forms of the projectile.

The indicating system of the invention comprises a projectile body preferably including a casing '20, a rotating band 2! near the tail end of the casing'and a nose 22 threaded into the casing. The projectile is loaded in a gun '23 hav-' ing a bore 23a provided with the usual rifiing cartridge case 24 containing the firing charge,

although it will be understood that th firing charge may be packed in bags in the gun chamber and the case 24 eliminated. At the rear of the gun is the usual breech mechanism designated generally at '25.

In the nose portion 22 of the projectile is a generating unit 26 for generating an electrical potential through the action of a force resulting from firing the projectile. One side of the gen erator is insulated from the projectile and connected to a conductor 21, which is preferably a bare copper wire extending in coils from the nose portion of the projectile along the bore 23a and out the muzzle of the gun, the wire being held loosely at the muzzle by suitable means (not shown) so that there is no electrical contact between the wire :and the gun. The end of the wire remote from the gun is connected to one side of an indicating apparatus 28, the other side 01 which is connected through a wire 29 to the gun, whereby a closed circuit is formed from one side of the generator 26, through the wire 21, indicatingapparatus 28, wire 29, gun 23, and projectile body 20 to the other side of the generator.

7 In operation,whenthe gun is fired,the electrical potential built up by the generator 26 in the pro jectile is impressed across the indicating appa ratus 28 which provides a measure of the potential so that the magnitude of the force utilized in gen crating the potential maybe determined. From the values thus indicated by apparatus 28, phenomena incident to the conduct of the projectile asit moves through the gun barrel may be determined, such as acceleration, set back, etc. As the projectile moves along the bore 23a, the wire 21 is collected in coils in thenose of the projectile in a suitable insulated collector unit, which will be described in detail presently, so as to prevent contact between the wire and the gun with a resulting short-circuit of the indicating appa ratus. The apparatus 28 may include an oscillograph operated by the electric charge from the projectile, and a camera for recording the operation of the oscillograph. It will be understood that instead of including the indicating apparatus in a closed circuit, as shown, the said apparatus may take the form of a receiving set responsive to the electric charge in the wire 21, whereby the connection 29 to the gun may be eliminated.

The projectile shown in Figs. 1 to 6 inclusive comprises an inner cup 3|, which may be made of steel,--located in a recess in the nose 22, the cup having its open end facing forward, and being held in the recess in any suitable manner, as by means of a press fit. Intermediate its ends, the cup is formed with an external shoulder 32 engaging the end of the nose 22. Within the cup 3| is an inverted inner cup 33 made of insulating material. such as Lucite. At the open end of the inner cup 33 is a metal base plate 34 connected to the inner cup by screws 35. The forward end of the plate 34, which is reduced, fits closely in the cup 33 and engages a copper disc 36 disposed between the said plate and electricity generating means comprising a piezo-electric crystal 31 surrounded by an insulating retaining washer 38. In front of the crystal 31 is another copper disc 39 disposed between thecrystal and a metal block at fitted closely in the cup 33 and movable relative thereto.

The interior of the outer cup 3| is enlarged at its open end to provide a shoulder 42, and seated in the enlargement on the shoulder is a collector unit comprising an insulating cup 43 held in position by a set screw 44 with the open end of the cup 43 facing forward. A cup-shaped collector electrode is held in the cup 43 with the open end of the electrode facing forward, the electrode being provided with an external shoulder 46 engaging the nose end of the cup 43. The inner wall of the electrode cup converges from the front of the cup to a plane intermediate its ends, as

' shown at 45c, and then diverges outwardly to the bottom of the cup, as shown at 451). If desired,

the collecting electrode 45 may be a simple cylindrical cup.

The collector or take-up electrode 45 is electrically connected to the block 46 by a connection comprising a plug 48 held in the insulating cup 43 and having a stem 49 in the electrode 45. The plug 48 has a spring contact 56 received in. a socket 5| in the closed end Of the insulating cup 33, the latter being provided with a recess 52 for receiving the socket. If desired, the insulating cups 33 and 33 may be cast around the socket 5| and plug 48, respectively. The socket 5| is connected to the block 46 by a conductor 53 extending through a passage in the cup 33; A screw 54 driven into the bottom of the collector electrode 45 provides a terminal for connection to the coiled wire 21 leading to the indicator 28.

When the gun is fired, the projectile accelerates in the bore 23a and causes the block to exert a force of setback against the crystal 31. As a result, an electrical potential difference is generated by the crystal and is impressed across the indicator 26 from the block 4.6 through conductor'53, socket 5|, plug 48, electrode 45, and wire 21, and from the base plate 34 through the outer cup 3|, the projectile body 2022, gun 23, and wire 29. Accordingly, the indicator provides a measure of thevoltage generated by the crystal 31, from which the force of setback of the block 40 may be computed. Since the mass of the block is known, the acceleration of the projectile as it moves along the gun bore may be determined. The coiled wire 21, as the projectile moves along the bore, is collected in the electrode 45, the conical surface a serving to direct the coils into the bottom portion 45b of the electrode where they are held by the restricted portion of the electrode. The collector unit 43-4-5 may be readily removed from the projectile by loosening the set screw 44, the plug and socket 48--5| providing a releasable electrical connection between the collector unit and the block as. When the parts are assembled, the collector'unit 4345 holds the inner cup 33 firmly in the outer cup 3 and the electricity generating means, the block to and the plate 34 are held securely in the inner cup.

The projectile shown in Fig. '7 is generally similar to that shown in Fig. 3 but includes means for counteracting the effect on the piezo-electric crystal of extraneous influences, such as vibration of the case 56 or the force of setback on the parts. In the projectile shown in Fig. '7, the nose portion 22a is provided with a recess for receiving a metal cup 56, which is held in the recess with the open end of the cup facing forward. Intermediate its ends, the cup is provided with an external shoulder 51 engaging the end of the nose 22a. Within the cup 56 is a metal case 58 s. cfcylindrical form inadeof aluminumor other metal. The ends of the case are threaded to receive metal plugs 59 and warespectively', the plugs having reduced porticns 6a and 60a, respee tivel-y, extending into the interior or the case 58 The plugs are adjustable in the case, and, to this end, may be provided with openings 6| for reeeiw ing a wrench. An insulating sleeve 62; which may be made of Lucite, is disposed in the case 58 between the reduced pertains 60 and 60a of the plugs; the sleeve containing a metal block 63' held closely in the sleeve but movable relative thereto. At the ends of the block are copper discs 64 which engage piezo-electi ic crystals 65 and 56 clamped between the discs 64 ands'iinilar discs amen the reduced plug portions 60 and 60a, respectively.

The interior of the cup 56- is enlarged at its open end to receive a ceuecter unit 43a=65a similar to the unit fil -45 in Fig. '3, the unit being seated on a shoulder 42a in the cup '56 and held in position by a set screw 44a. The collector electrode 45a is electrically connected to the block 63 through a connection comprising a plug 480. in the insulating cup 43a, the plug having a stern 49a extending into the electrode. A sprin contact 50a of the plug is received in a socket m. in an insulating plug 61 disposed in a recess in the case 56 at one side of the sleeve 62. A coirduetcr 68 extends from thesocket 5m through a passage in plug 61 to an opening 69 extending transversely through the plug and the case to the sleeve 62. An insulating bushing 70 in the opening 69 has a recess in its outer end portion in which the conductor 68 is connected to another conductor H extending inwardly through the bushing and through an aligned opening in sleeve 62 to the block 63. In its inner end portion, the bushing has a conical recess 12 which flares toward the block 63 to permit movement of the block relative to the bushing without injuring the electrical connection to the block. A screw 54a in the collector electrode 45a serves as a terminal for connection to the wire 21 leading to the indicating apparatus.

In the use of the projectile, the plugs 56- 5% are tightened in the case 58 so as to force the crystals 65 and 66 against block 63 and subject them to an initial compression. The crystals are arranged in opposing relationship so that the potential difference generated by crystal 65 tends to counteract that generated in crystal 66, and to this end the positive side of one 'of the crystals and the negative side of the other crystal are disposed adjacent the block 63. The plugs 59 and 59a may be adjusted i-nthe case by loosening set screw 44a removing the collector unit cu-45a, raising the case 58 from cup 56, and applying 'a wrench to the plugs. When the plugs 59-59(1 have been adjusted, they may be locked in their adjusted positions by set screws 13 in the case 58, after which the parts are assembled as shown.

When the projectile is fired, the force of setback of block 63 causes the block to increase the pressure on crystal 6B and decrease the pres-sure on crystal 65, whereby the block is charged more highly with a charge corresponding to that on the adjacent side of crystal 66-, while the projectile is charged more highly with an opposite charge through the plugs Ell -59a, case 58 and cup 56. It will be observed that the charge placed on block 63 by a change in the pressure on crystal 66 due to either a positive or a negative force of setback is of the same sign (1. is. positive for a positive setback and negative for a negative 6. setback) as that placed on block 63 by the resulting opposite change in the pressure on the other crystal 65. The potential thus generated is impressed across the indicating apparatus 28 from the projectile through the gun 23 and wire 29, and from the block 63 through conductors H and 68, plug and socket 46a, em, electrode 45a and wire 21.

When the projectile is fired, an vibrations or other forces therein tending to affect the potentials generated in crystal 66 by the setback force of block 63 also produce in the crystal 65 an equal change in potential which opposes the change in crystal 66. Accordingly, these Vibrations or other forces have no efiect on the ultimate potential difierence generated between the block 63 and the projectile. Also by reason of the opposing crystals 65-66, the generator compensates for changes in prestressing thereof due to adjustment of the plugs 59-5612. In the event that the case 58 is compressed by the force of setback, the resulting increase in pressure on crystal 66 is counteracted by a corresponding increase in the pressure on crystal 65, so that there is no change in the indicated voltage. Since the crystals 65 and 66 are arranged to produce opposite charges on the block 63 when they are compressed, a positive setback generates a positive charge on the block relative to the projectile body 2%, andthe gun 23, and a negative setback generates a negative charge on the block with respect to the projectile body 22a and the gun 23-. Accordingly, both positive and negative setbacks may be measured. The case 58 is preferably made of aluminum so as to increase its resonant frequency, whereby its vibrations will have substantially no effect on the generated potentials.

The projectiles shown in Figs. 11 and 12 are similar in principle to those illustrated in Figs. 3 and 7 but are suitable for use in measuring the pressure to which the tail end of the projectile is subjected by the explosion of the firing charge in the gun. The projectile shown in Fig. 11 com prises a body including a case 22b having the usual rotating band 2 lb and nose 221). At its tail end, the projectile is held n a cartridge case 2% containing the usual firing charge 75. Mounted in a recess in the tail end of the projectile is a cup-shaped cylinder 56 made of insulating material, such as Lucite, the open end of the cylinder facing to the rear. A metal plunger 11 fits closely in the cylinder and is movable thereinv Secured to the openend of cylinder 16, as by means of screws i8, is a retaining plate 19 for the plunger. The plate 79 also serves as a bafile and, to this end, is provided with a plurality of lateral ports 80 communicating with a central longitudinal passage 8! leading to the plunger. Between the inner end of the plunger and the inner end of cylinder 16 is an electricity generating means comprising a piezo-electric crystal 8-2, the generating means being similar to that shown inFig. 3. One side of the crystal. 82 is grounded to the projectile body, as shown at 82a, and the other side is connected through a conductor 83a on the plunger to a terminal 83 held in the wall of cylinder 16. The terminal projects from cylinder 16 into a recess 84 in the projectile where it is connected to a Wire 85 extending through a pas sage 64a in the projectile into the main chamber of the casing 232:. The Wire 85 is insulated from the projectile and is connected near the nose thereof to the terminal 53b of a collector unit 4312-4519 similar to that shown in Figs. 3 and. '7.v

follower 96.

sure

: Upon firing the projectile ina gun, the pressure resulting from the explosion of the firing charge is communicated through the ports 80 in the .baffie to plunger 11 and forces the plunger against crystal 82 so as to generate an electrical potential difference between the opposit faces of the crystal. The electric charge built up by the crystal as a result of the explosion of the firing charge is impressed across the indicator through wire 83a, terminal 83, wire 85, terminal 54b and wire 2'"), and through the projectile body 29b, g'un 23 and wire 29.

-- In the projectile shown in Fig. 12, the casing 2Dc'carries a rotating band 2 lo and a nose portion 220, and the tail end of the casing is held in a cartridge case 240. In its tail end, the projectile has a recess for receiving a metal case 81 which may be held in the recess in any suitable manner. Outside the recess, the case is formed with an external shoulder 86a engaging the rear end of the projectile. A cylinder 88 secured in the tail end of the case 81 is provided with an externally threaded boss 880. on which a baflle element 89 is screwed, the baffle element having ports 89a for admitting pressure fluid resulting from explosion of the firin charge in the cartridge case. Slidable in the case 81 in front of the cylinder 88 is a metal block 99 having at its rear end a plunger 9| in the cylinder, the plunger being preferably connected to the block by releasable means, such as a threaded stud 92. An obturator 9|a, which may be made of Duprene, or the like, is disposed on the free end of the plunger. Seated in the front end of block 90 is the dome portion of a hemispherical element 93, the base of which engages a piezo-electric crystal which, as shown, is

made up of a plurality of quartz discs 94. The discs 94 are retained in an insulating sleeve 95 within the case 81 and are interposed between the hemispherical element and a metal follower 96 in the sleeve. The front end of sleeve 95 is closed by an insulating disc 97 engaging the adjacent face of the follower, and the disc 9'! is clamped against the sleeve and the follower by a metal plug 98 threaded into the front end of case 81.

The plug 98 is provided with a central opening for receiving an insulating collar 99 through which the shank of a terminal post I90 extends, the rear end of the post being imbedded in the At its front end, the post I is connected to an insulated wire 85a extending through the chambered interior of the projectile -to a terminal screw 54c mounted at the nose of the projectile on an insulated collector unit 43c45c. The terminal 540 is designed to be connected to one side of the indicator 28 by the coiled wire 21 extending through the bore of the gun, the other side of the indicator being connected through wire 29, gun 23 and the projectile body to the other side of the generator 94.

The operation of the projectile shown in Fig. 12 is generally similar to that of the one shown in Fig. 11. When the projectile is fired, the presfrom the explosion is directed against plunger 9|, the baffle 89 preventing solid powder grains from striking the plunger and producing spurious signals. The plunger then compresses the crystals 94 through the block 90 and the hemispherical element 93, which provides uniform loading of the crystals. If desired, thin sheets of annealed copper (not shown) may be placed between adjacent faces of the crystal discs 94 to distribute the load where there are minor irregularities in the surfaces of the crystals. As

a result of their compression, the crystals 94 generate anelectrical'--- potential diiference, one charge of which is conducted through an insulated conducting path comprising follower 96. post- I00, wire a, terminal 540, and wire 21 to one side of the indicator. The opposite charge is conducted from the hemispherical element 93 through case 81, the projectile body, the gun, and wire 29 to the other side of the indicator.

If desired, the cylinder 88 and plunger 9| may be removed and replaced by a cylinder and plunger of different size so as to provide a new ratio between the mass of the moving parts in the projectile and the area of. the plunger, to correspond with the new mass to area ratio of a different projectile, whereby measurements for projectiles of several different sizes may be made with the same electricity generating means.-

The use of the invention may be more readily understood by reference to the following relations: Y r

According to Newtons law the forces on a projectile of mass M and cross-sectional area A are (1) M a=PA=R, wherea is acceleration; Pis pressure, and R is bore friction. Also, the force on the plunger 9| is (2) ma=PB-F, where m is the mass of the plunger; a is the acceleration of the plunger by confinement in the projectile; P is pressure; B is the area of the plunger, and F is the force of the crystal on the plunger. Solving for the acceleration and equating (1) and (2):

With the mass to area ratio of the projectile equal to the mass to area ratio of the plunger 9|, the terms involving pressure will cancel, leaving In the foregoing it is assumed that there is no effect of friction on the. plunger, which is a reasonable assumption since the plunger is confined and clearances are relatively large. Accordingly, the effect of pressure is eliminated, and only known or readily measurable values are involved.

From measurements made while pushing a rifling band through a forcing cone, it is reasonable to expect a maximum friction force of about 25 tons between the projectile and the gun barrel. In a 3" projectile having a mass 12.8 lbs. and containing a plunger 9| having a mass of 0.2 1b., the force on the piezo-electric crystal according to Equation 3 is With four quartz crystals 94 of a Curie constant,

K,'of 8.5x 10- coulombs, Q, per pound, the maximum signal to expect is There are a few obvious sources of error in the new system, but their importance may be determined so that they may be properly evaluated and corrected in the mathematical calculations based on the readings of the indicator. One possible error is mismatching of the mass to area ratio of the plunger and the projectile. This may be corrected by drilling out a portion of the plunger to adjust its mass. If an error still exists, its effect on the calculated results may be counteracted on the basis that the size of the error is PEB, where P is the pressure acting on the plunger 9|, Bis the area of the plunger, and

E is the assumed percentage error in matching. Another possible source of error is the bafile 89, which may produce a hysteresis efieet caused by a retarded action on the plunger of the gas pres.- sure which produces the signal. Since the gas is piling up and not flowing straight through the baflle, the error Will probably be one due only to the increased length of the path, which error is of the order of microseconds. Another possible error is that caused by loosening of the electricity generating assembly due to the spin of the projectile. To prevent such loosening, the threads on the parts in the assembly may be so arranged that the spin tends to tighten them so as to hold the parts more firmly. The end plate members 9|-.-98 adjacent the crystals 54 are thick enough to prevent any substantial deflection and compression of the crystals under the maximum load imposed by the set back force of the explosive charge in the projectile.

It will be evident that the system of this invene iiOl' may be used for several different purposes. For example, it may be used for timing parts of iuzes or safety devices in the projectile and for determining the acceleration of the projectile, vi-

bratiens of the parts of the projectile or fuze, the pressure on the base of the projectile, the friction between the projectile and the bore of the un, the leakage of gas past the projectile in the gun, angular acceleration of the projectile, the strains produced in various parts of the projectile or ruze, or the temperature of the rotating band and the bore of the gun while the projectile is moving out of t un.

We claim:

1. In combination, a gun barrel, a projectile adapted to be fired from the gun barrel, means in the projectile for generating an electrical potential difierence upon movement of the projectile through the gun barrel, an electrical indicat-.- ing device remote from the gun barrel, and conducting means including a conductor extending from the projectile along the bore of the gun barrel and connecting the generating means to the indicating device.

a 2. In a projectile having a body, an insulating container in the body, a base plate, electricall} connected to the body a member in the container movable relative to the container, a quartz crystal between the movable member and the base plate, said member being movable upon acceleration or the projectile to compress the crystal and cause the crystal to generate an electrical potential difference commensurate with the set back force acting on the member, a collector terminal mounted on the body and insulated therefrom, an electrical connection between said movable member and the terminal and i i-.- sulated trom the body, for taking up said electrical connection during the travel of the projectile while being fired, and means connected to said body and said terminal respectively, for measuring said potential difference.

3, In combination, a gun barrel, a prqjeetile adapted to be fired from the gun barrel having a body, means in the projectile body for generate ing an electrical potential difference upon movement of the projectile through the gun barrel, an electrical connection between said body and one side of the generating means, conducting means connected to the other side of the generate ing means and insulated from the body, said conducting means extending along the interior of the gun and projecting therefrom, a container carried by the proj til o tak ng p and t9r- 1.0 .5 midonduc ing m ans, and an ndica or lse: ica o ected to th gun and to, Said con..- du t n m an and u s de he tra ec o o he projectile, for providing a measure of said peter}:- tial difference. 1

{1. In combination, a gun barrel, a projectile dapted to be f ed om t un barr l aving a bo y. means i h ojectile bo y fo ge a ing an electrical potent al difference upon move men of the project l th ugh h un b r l n electrical connection between said body and one side of the generating means, a collector unit at e nose e the p o ect a d lated m b dy a conducto extendin from said Unit ugh the bore of the gun, said unit including a container for taking up and storing said con doctor, an electrical connection between the other side of the ge eratin me s a d h ctor and insulated from said body, and an indicator el t ica ly co nected to th u and to s id cone doctor for providing a measure of said potential diiference, said indicator being located outside the trajectory of the projectile.

5. A projectile comprising a bod-y, a hollow col-,- lecter -ie s cur d to tbe l d at t s at he projectile and insulated from the body. a termit- 1 a n the i l ee er unit stee t i me ns in the body for g nerating an e ctrica p t ntial difference on firing oi the projectile, an electriw al csn e t on bet en e side o th eneratin means and the terminal and insulated from the body, and a e ctr a c nnec ion e w n the th s d of t gene at ng m ans an he ar.-

6- In combin tion. a gun barrel. a project le adapted to be fired from the gun barrel, means it} the projectile for generating an electrical poten l s ll-T e ce u on nw e ent 9 th arpiectile hro h h un ba r an el c ric ind catin e i e emot imam th un barrel. conducting means includin a mil s ondu tor xtendin from the projectile along the bore of the gun bar rel ior impressing said potential difference across the indicating means, and a ,collector unit at the nose of the projectile for receiving said conductor the. pr ect le m es lo he u arre A p ojec ile co r ng ody. a ondu ing m mber n t e b d met e r at e t ereto on. acceleration o the p o ec le a m -e ectric quartz crystal ,at eachend of said member, a conudin eleme t ng gi eac crys al theiace emo e tram said em e he c tal bein no ia l-y st essed b twee sa d memb r and he cone du tin e em nts, said crystals, n ctin 3% h and c nd cti elements m n a ean for en at n lectrical potential ,difierence 0i ,in cr as ng magnitud as, the o ce Q Set ad; of said member increases, an electrical connection be w n e beer an ne si Q aid eratin means, and aneleetr cal c nection ex nd g om the r s of sa d atin m ans it the outside of the body and. insulated from the bo y.

8. A projectile comprising a body having a re: ces in its nose end, a general y phaped in? sulating container disposed in the recess with the p n d of he wn ain r a in the tail nd of the projectile, a metal block in the container ad, iacent the ba e th e f. a n zceele tr c rysta in the ontai e adjac n e a and of t e blo k, a plate a iaeeni the all ace o the m n and le tr a l c n ete o the o a en rall can-sha es colle tor secu ed 1 9 e-bod it front of the container with the open end of the unit t the n se oi th prpe t le. a d un be ng e etin el ment :iil

nsula ed fr m the eer the collector unit, an electrical connection extending from said block through the base of the container to the conducting element, and an indicator connected to' said body and to said conducting element.

I 9. A projectile comprising a body, means in the body for generating an electrical potential difference on firing the projectile, an electrical connection between the body and one side of the generating means, a generally cup-shaped collector unit disposed at the nose of the projectile with the open end of the unit facing forward, releasable means for securing said unit to the body, said 'unit being insulated from the body, a releasable electrical connection extending from the other side of said generating means into the collector of the body, a metal block in the container, a

piezo-electric crystal in the container adjacent each end of the block, a conducting member adjacent each crystal normally pressing the crystal against the block and electrically connected to the body, conducting means extending from the block intermediate the ends thereof through the container to the outside of the body, means for insulating said conducting means from the body, a generally cup-shaped collector unit disposed at the nose of the projectile with the open end of the unit facing forward, said unit being insulated from the body, a conducting element in the collector unit, electrically connected to said conducting means, and an indicator connected to said body and to said conducting element.

11. A projectile comprising a body having a recess in the nose end, a generally tubular insulating container in the recess extending lengthwise of the body, a metal block in the container, a

piezo-electric crystal in the container adjacent each end of the block, a conducting member threaded in the body adjacent each crystal for pressing the crystal against the block and electrically connected to the body, the conducting member being adjustabl to varythe compression of the crystals, conducting means extending from the block intermediate the ends thereof through the container to the outside of the body, means for insulating said conducting means from the body, a generally cup-shaped collector unit disposed at the nose of the projectile with the open end of the unit facing forward, said unit being insulated from the body, a conducting element in the collector unit, electrically connected to said conducting means, and an indicator connected to said body and to said conducting element.

12. A projectile comprising a body having a recess in the nose end, a generally tubular insulating container in the recess extending lengthwise of the body, a metal block in the container, a piezo-electric crystal in the container adjacent each end of the block, a conducting member ad-, jacent each crystal normally pressing the crystalagainst the block and electrically connected to the body, an insulating plug in the body adjacent the container, conducting means extending from the block intermediate its ends through the side wall of the container and through said plug to the outside of the body, a generally cup-shaped collector unit disposed at the nose of the projec- 12 tile with the open end of the unit facing forward, said unit being insulated from the body, a conducting element in the collector unit, electrically connected to said conducting means, and an indicator connected to said body and to said conducting element.

13. A projectile comprising a body having a re-' cess in its tail end, a cylinder of insulating ma.- terial in the recess, a plunger in the cylinder, a piezo-electric crystal in the cylinder adjacent the inner end of the plunger, the plunger "being operable by fluid pressure against the tail end of the projectile to compress the crystal and cause it to generate an electrical potential difference, and an electrical connection extending from the plunger through the body to the outside of the projectile for conducting a charge from the crystal to the nose, said connection being insulated from the body.

14. A projectile comprisinga body having a cylinder in its tail end, a plunger in the cylinder, a piezo-electric crystal in the bod adjacent the inner end of the plunger, the plunger being operable by fluid pressure against the tail end of the projectile to compress the crystal and cause it to generate an electrical potential difference, one side of the crystal being electrically connected through the plunger and cylinder to the body, an electrical connection extending from the opposite side of the crystal through the body to the outside of the projectile, and means for insulating the crystal and said connection from the body.

15. A projectile comprising a body having a cylinder in its tail end, a plunger in the cylinder, a hemispherical element having its dome portion seated in the inner end of the plunger, a piezoelectric crystal in the cylinder adjacent the base of said element, the plunger being operable by fluid pressure against the tail end of the projectile to compress the crystal and cause it to generate an electrical potential difference, an electrical connection extending from one side of the crystal through the body to the outside of the projectile and electrically insulated from the body, a generally cup-shaped collector unit disposed at the nose of the projectile with the open end of the unit facingforward, said unit being insulated from the body, a conducting element in the collector unit, electrically connected to said electrical connection, and an indicator connected to said body and to said conducting element. 16. A projectile comprising a body having a cylinder in its tail end, a plunger in the cylinder, a piezo-electric crystal in the cylinder adjacent the inner end Of the plunger, baffle means on the projectile for directing fluid pressure from the tail end of the projectile against the plunger to cause the plunger to compress the crystal and generate an electrical potential difierence, an electrical connection extending from one side of the crystal through the body to the outside of the projectile and electrically insulated from the body, a generally cup-shaped collector unit disposed at the nose of the projectile with the open end of the unit facing forward, said unit being insulated from the body, a conducting element in the collector unit, electrically connected to said electrical connection, and an indicator connected to said body and to said conducting element.

1'7. In a projectile having a body, an insulating container in said body, means in the container for generating an electrical potential difference in response to firing of said projectile, one side of said generating means being connected electri 75 cally to-the. projectile body, acollectorterminal- 13 mounted on said bod and insulated therefrom, means insulated from the body and electrically connecting said terminal to the other side of said generating means, an electrical conductor also connected to said terminal, said terminal taking up said conductor during the travel of the projectile while being fired, and means for measuring said potential diiference, connected to said conductor and to said body respectively.

NICHOLAS M. SMITH, JR. J. ALLEN CROCKER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,755,023 Ruhleman Apr. 15, 1930 1,917,813 Ruhleman July 11, 1933 1,919,480 Rieber July 25, 1933 2,064,489 Neuman Dec. 15, 1936 Number Name Date 2,068,744 Gutzke Jan. 26, 1937 2,096,826 Schrader Oct. 26, 1937 2,137,852 Nicolson Nov. 22, 1938 2,250,496 Postlethwaite July 29, 1941 2,256,406 Muir Sept. 6, 1941 2,275,256 Fried Mar. 3, 1942 2,315,756 Warner Apr. 6, 1943 2,371,626 Kecskemeti Mar. 20, 1945 2,405,597 Miller Aug. 13, 1946 FOREIGN PATENTS Number Country Date 404,622 Great Britain J an. 12, 1934 473,636 Great Britain Oct. 18, 1937 719,762 France Feb. 10, 1932 OTHER REFERENCES Tschappat, W. l-I.: article on Experiments in 20 Interior Ballistics, published in Mechanical Engineering," Aug., 1926, vol. 48, N0. 8, pp. 819 through 825. 

